In containers using threaded closures where either the container or closure or both are made of a resilient plastic material, slippage or loosening of the closure from the container, normally classified as “backing off”, can occur. This backoff effect is typically caused due to several factors. Resilient plastic materials inherently posses the ability to flow or creep under stress or pressure which results in a gradual loosening of the closure on the neck of the container. The closure may loosen from the container due to the internal pressure of the packaged product or pressures involved in air transport of the product. The low co-efficient of friction and self-lubricating qualities of plastic materials normally used in molding typical closures and containers can cause slippage. Minor manufacturing defects that occur during the molding process can create misalignment problems between the closure and the container that lead to backing off. Most commonly, with the above properties vibrations that occur during shipping and handling of the containers can cause the closure to backoff.
Backing off can be a significant problem to packagers in that containers having closures which are loose or appear to have been opened are less likely to be selected by consumers for fear of tampering or contamination. Further, the contents of the container can become spoiled and the product becomes unsalable, which results in a complete loss to the product manufacturer, distributor, or retailer. All in all, the effects of backing off can cost a manufacturing, packaging, distributing or retail business a substantial amount of money.
Thus far, most of the solutions to the costly problem of closure backoff have either failed or are too expensive, too inconvenient or too complicated to work in the closure cap and container manufacturing processes. Some of these solution include the addition of appendages which mate with the container, grooves or recesses, and a system of complementary ridges and recesses. These solutions typically require retooling and redesign of molding dies and stamping machinery, and therefore, are not acceptable to manufacturers. While many of the solutions and other types of closures have proved satisfactory in many respects, nevertheless, there is still a need for a container closure which provides a long term retention of the initial torque used to apply the closure to the container. The present invention provides such a closure assembly which resists subsequent loosening, or backing off, of the closure from the container.